The invention relates to implants for subcutaneous or intradermal injection into fibrous tissue, for use in man or animals in reparatory or plastic surgery or in esthetic dermatology for filling wrinkles, fine lines, skin depressions and scars, including the filling of skin defects secondary to the taking of a treatment liable to result in a lipodystrophy usually characterized by facial lipoatrophy.
A certain number of products have been used to date. Each product has advantages and disadvantages.                Silicone oils, which are banned as injections, were easy to use. However, migration of droplets of silicone into the tissues located below the point of injection, by simple gravity, has been observed after injection. Silicone incorrectly used or used in large amount has been the cause of siliconoma, and even of delayed allergic reactions. Silicone is not biodegradable.        Teflon® paste is a suspension of polytetrafluoroethylene microparticles (diameter from 10 to 100 μm) in glycerol. This product, in many cases, caused severe and chronic serous infections and had to be removed after a few months from the dermal and subdermal tissues for the majority of patients. It has also been proven that small polytetrafluoroethylene microparticles were found in the liver.        Collagen suspensions have been very widely used in the last ten years. Collagen has remained the leader in these indications for a very long time since it was virtually the only product used that benefits from a marketing authorization for the treatment of aging of the skin. A few cases of allergic reactions have been noted in about 3% of patients. The resorption of collagen occurs on average in the majority of patients between 3 and 5 months, which necessitates several injections per year in order to have a certain level of efficacy. Finally, it should be noted that collagen is of bovine origin.        Biological samples taken from the patient himself. The idea was, admittedly, interesting, but the clinical experience revealed the failure in reimplanting fatty cells, which are absorbed and disappear within a few weeks. Another system consisted in adding plasma from the patient to a collagen gelatin of bovine and porcine origins. The results are even more disappointing and the product is of animal origin.        Hyaluronic acid used in the majority of pharmaceutical forms or in the majority of medical devices is in the form of a sodium hyaluronate gel. It is, very widely used by virtue of its ease of injection and its safety of use, and it offers a good alternative on account of its biocompatibility and its absence of toxicity. These sodium hyaluronate gels are moreover widely used in eye surgery. However, their rapid bioresorbability (typically ranging between 4 and 6 months) may disappoint certain users in the field of filling wrinkles or skin depressions, since the injections must be repeated at close and regular intervals.        Bioplastics are polymerized silicone microparticles (diameter 70 to 140μ) dispersed in poly-vinylpyrrolidone. Rejection reactions have been noted.        Polymethyl methacrylate (PMMA) microspheres 20 to 40 μm in diameter in suspension either in a gelatin solution or in a collagen solution or in a hyaluronic acid solution. PMMA is not biodegradable, although widely used in the field of ophthalmology in the form of an intraocular implant. In the dermato-esthetic field, there is not sufficient history to know how this implant behaves after five or six years of intradermal implantation. Moreover, when the vector is a collagen solution (of bovine origin), allergy has been reported in 3% of cases.        Polylactic acid (PLA) microparticles of poly-morphic form and from 40 to 63 μm in diameter in suspension in sodium carmellose. The product sold under the name Newfill® represents advantageous progress since it allows efficacy of treatment over a relatively long period, limiting the injection sessions. The polymer used is an L PLA 100 (crystalline form of 100% levorotatory PLA) that incurs extremely slow resorption kinetics (more than 5 years). However, the persistence of PLA crystals in the tissues may be feared, which may, in certain cases, lead in the long term to chronic inflammatory reactions during repeated injections. The use of CMC (cellulose derivative) may, on the one hand, be the cause of allergic reactions, and, on the other hand, the body does not have an enzymatic system capable of degrading cellulose. Furthermore, extemporaneous reconstitution, vigorous shaking for homogenization before use, and poor syringeability of the product limit its use and put off many users. Cases of granuloma at two years and also cystic nodules requiring exeresis in the majority of cases are beginning to be reported.        